I have done this before, and usually I work with one provider who coordinates with all the others. In some instances the rate would be the same for all. In other instances there was has been a slight difference in rates. The coordinator leaves it up to me to determine whether or not I’m willing to pay their individual rate
I put each payment in an envelope with their name on it and leave it up to him to hand out. In some instances I do. If the organisation took extra time and if coordination was more complicated for the coordinating provider I usually increase their rate a bit to cover their time and efforts to bring the group together.